Which turbine is the most efficient?
We have heard questions about turbine efficiency a few times. Usually it is in the context of a discussion over choice of turbines (eg - which of your turbine options is the most efficient?) so I'll talk about that today.
Occasionally the question is asked more from the point of view that any turbine is inefficient therefore we shouldn't build them, this is essentially a windfarm myth and is a topic for another day. Today's post will be recommended reading for that discussion.
So - a question about efficiency can only be answered by considering how you are going to measure efficiency. I can think of at least three ways to do this:
1. Efficiency of land use
2. Efficiency of energy capture
3. Economic efficiency
Land use
By this I mean, how much energy you can collect from the area of land available. Energy collection is mostly about rotor area (ie how much swept area of rotor can be fitted on the site). On Mt Cass we can only fit a single row of turbines and so, the bigger the turbine the more swept area we can install. If efficiency of land use was our main objective then the choice of turbine would be clear. The bigger, the better.
Energy Capture
Efficiency of energy capture is often expressed by the 'capacity factor' of a particular turbine or group of turbines, for example we hear the the Manawatu windfarms are among the best in the world with capacity factors of around 50%. (capacity factor is the total energy output of a wind farm as a proportion of the theoretical maximum output if a windfarm ran at full production all the time). But, 'capacity factor' really just measures how much the generator is used and to some extent is a choice of the turbine designer (ie a small generator with a big rotor will always have a higher capacity factor than a big generator with a small rotor). This would be fine if all turbines had the same ratio of rotor diameter to generator size, or, if the generator was the main cost driver of a wind turbine, but, they don't, and, it isn't.
The main driver of turbine cost is rotor diameter. The rotor size tends to dominate all the loads throughout the turbine mechanism and structure and therefore drives the weight and the cost of the machine. There is another measure of turbine efficiency called 'specific energy' which is arguably a more useful measure of turbine efficiency because it relates to the amount of energy captured by the rotor.
If we were choosing based on 'capacity factor' the big turbines would again be a clear choice. But, if we base our assessment on 'specific energy' then the small Windflow turbine becomes a contender.
Economics
What we are most interested in is economic efficiency of our windfarm (assuming any turbine we choose is technically appropriate for the site). Why? because, for a start it will mean the project has the best chance of getting up and running, Then, when running, it means the windfarm will give a payback to MainPower and our shareholders, the community.
To determine economic efficiency we have to look at the cost of the turbines and the windfarm as a whole. Not just the initial build cost but the long term expectations of operating and maintenance too.
That sort of information can only be gathered through a formal tender process, after we have a resource consent.
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Comments
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Synchronization, is there much difference in the cost of synchronizing to the grid between Windflows Synchronous generator and the other larger unsynchronized generators?
Posted by Lindsay Russell, 08/09/2007 8:28pm (3 years ago)
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In a word - "Yes". This is one of Windflow's benefits along with things like lower cost, lighter equipment (hence smaller cranes etc).
There may also be the prospect of selling 'voltage support' services using the synchronous generator which could improve windfarm revenue.
But, on this site the big turbines appear to produce more energy, so to a certain extent we can afford to pay for the extra electronic equipment etc that they need.Posted by Andrew Hurley, 10/09/2007 9:39pm (3 years ago)
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Would windflow produce a larger turbine? It seems preferable to use a larger turbine for its efficiency and more efficient use of infrastructure related to access and conveying power from Mt Cass to the Waipara sub station. There seem to have been some poor quality large turbines produced in Europe as a result of subsidies inducing high demand.
Posted by Julian Ball, 11/09/2007 5:10pm (3 years ago)
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A large Windflow??..hmmmm. there is no reason why they couldn't produce a larger Windflow turbine. The basic principles of the gearbox and teetering rotor can be upscaled. But it would be a big shift in their focus and realistically couldn't be achieved without a few years of effort.
There may also not be too much motivation for them to do this because the capacity penalty they have on this site is more a result of the site than the turbine.
For any site where you can fit more than one row of turbines the total installed capacity is similar for any turbine size.Posted by Andrew Hurley, 12/09/2007 12:31pm (3 years ago)
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If you do need to go with the larger turbines could you also use some Windflows as well to do the synchronizing?
Posted by Lindsay Russell, 13/10/2007 9:26pm (3 years ago)
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Nice to see someone in your position use a blog to discuss these kind of issues Andrew.
My personal preference is for larger turbines because as you say the difference between small and large turbines is relatively small compared to before and after a wind farm (of any size).
Having gone through all the effort to set up the project, I believe its best to make the most of it. So long as you point on efficiency point that way.Posted by James, 20/10/2007 9:46pm (3 years ago)
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Hi Lindsay
Sorry - I've had my eye off the blog for a while (as I tend to all our technical reports).
There's a couple of reasons why we can't do as you suggest (ie incorporate a few Windflows).
1) It seems to be a visual "no-no" to mix an match wind turbines in one development - but then again they have done it at Tararua. but....
2) even if we had a few Windflows in the mix it wouldn't help the rest of the trubines sychronise. They would still have to do the AC-DC-AC conversions and synch via electronic means.
What Windflows would achieve if mixed in is some ability to provide voltage support (reactive power).
Well known local engineering identity David King also pointed out to me on Friday that the Windflow can run 'islanded' (ie without the grid) which could be seen as a benefit of their design (and definitely is a benefit in other circumstances).Posted by Andrew Hurley, 29/10/2007 11:04am (3 years ago)
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James - thanks for your comments and for expressing a preference. As indicated above I'll make sure I'm watching a bit closer from now on.
Posted by Andrew Hurley, 29/10/2007 11:05am (3 years ago)
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The Foote Creek Rim wind farm in Wyoming is a good example of a well placed, high functioning, economic wind farm. The annual average wind speed is 7.62 m/s. But the wind blows nearly steadily in the same direction. There are no trees, no bushes, not even a cow. There is a moderate rise in front of the turbine lines of about 100 m over 2 km. This is a good wind resource and a well placed and designed wind farm. There is a huge interstate highway just near by to bring in the equipment, but it's otherwise remote and un-loved land. There is a big grid to connect to. It was built in 1999.
Posted by Susan Krumdieck, 30/07/2008 7:12pm (2 years ago)
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Hi Susan
Sounds like a good site - I just don't think there are too many, if any, like this in NZ (as I think is partly your point).
I'd also hazard a guess that the Production Tax Credit has a fair bit to do with making the project economic.Posted by Andrew Hurley, 01/08/2008 9:55am (2 years ago)
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